This invention relates generally to ambulatory heart monitoring methods and apparatus. More specifically, it concerns a QRS complex validation method and an arrhythmia identification method used in improved ambulatory ECG monitoring apparatus that, by virtue of its power partitioning and management circuit, can monitor continuously and event record a patient's cardiovascular performance for an extended period of time.
Typically, ambulatory heart rate monitoring and recording equipment rely upon volatile semiconductor read and write memory (RAM) devices to store ECG data for later analysis. As they usually are battery-powered, such equipment have a recording capacity limited by the RAM's density, as well as by the life of the batteries, which must power not only the RAM but also the microprocessor the analog to digital converter (ADC), the clock and other digital and analog circuitry. Twenty-four or forty-eight hour ambulatory cardiac monitoring equipment--while truly portable to the extent that they are lightweight and self-contained--are extremely limited in their ability to monitor arrhythmia, which may not manifest for days or even weeks.
Various methods for accurately detecting, or validating, QRS complexes (as against motion or other artifacts) within a patient's ECG signal have been used in ambulatory cardiac monitoring equipment. Most rely on some form of ECG signal amplitude measurement, at least over a candidate QRS interval, and comparison with presumed physiological norms. Similarly, methods for determining when a measured heart rate or change therein is worthy of recording as an arrhythmic event (as against a normal heart rate acceleration or deceleration) have depended upon comparisons of measured heart beat intervals with presumed physiologically normal heart rates. Methods which presume norms not always in evidence with a particular patient involved in a particular activity are intolerant of idiosyncratic, but perfectly acceptable, cardiovascular performance. Such methods thus are error-prone.
It is desired to provide in ambulatory heart rate monitoring equipment a greatly extended ECG monitoring and reporting capacity, without unduly burdening the ambulatory patient or restricting the patient's freedom to move about. It also is desired to provide improved techniques for detecting and validating QRS complexes, thereby to produce more accurate and reliable monitoring and recording results. Finally, it is desired to provide improved techniques for determining when an arrhythmic or other abnormal cardiovascular event has occurred, thus reducing the likelihood of a false positive indication of cardiovascular dysfunction.
Accordingly, it is a primary object of this invention to provide an ambulatory heart data monitoring and recording device capable of continuously monitoring and selectively recording a patient's cardiovascular performance over an extended period of time.
Another object of the invention is to provide such extended monitoring and recording capacity without further burdening or inconveniencing the ambulatory patient.
Yet another object of the invention is to provide such a device with a power partitioning and management circuit that ensures the long and uninterrupted supply of power to potentially volatile data storage circuit elements.
Still another important object of the invention is to provide a QRS complex validation technique that adapts itself to the individual patient.
Another important object of the invention is to provide an arrhythmic event determination technique that is less likely to give false positive indications of cardiovascular dysfunction.
A further object of the invention is to provide such improved heart rate monitoring and recording cost-effectively.
These and other objects of the invention will be understood in reference to the following detailed description of the preferred embodiment and methods of the invention, and by reference to the accompanying drawings.